This invention relates to a microscope with an objective turret carrying a large number of objective lenses, in which a turret position located in the optical path of the microscope is assigned to each objective. A motor is connected to the objective turret so that it can drive the turret, and it can be switched off, automatically, in the individual turret positions.
Microscopes of this type are known which have an objective turret that can be rotated in either direction by means of a motor, that is to say which is reversible. A motor-driven turret is used to avoid contaminating the object to be examined, or even destroying it, which can occur in cases involving manual turret-rotation. Contamination can have extremely disadvantageous results, particularly when examining thin-film semiconductor structures which fall within the micron range.
In these known microscopes, the motor which drives the objective turret is connected to a double control key. This causes the objective turret to rotate in one direction when one of the keys is operated, and drives it in the other direction, forwards or backwards, when the other key is operated. When a double key is used in this way, the objective turret rotated for as long as this double key remains pressed. When this key, which is known as a plus/minus key, is released, the objective turret comes to rest in the next objective position.
When low-power objectives which exhibit a large depth of focus are being used, the insensitivity of the visual focussing adjustment can lead to the destruction of the object being examined. This can happen during the change-over, that is to say during rotation from a low-power objective of the above-mentioned type to a very high-power objective. When working with an unfamiliar microscope, it is not always possible to reliably prevent a collision between a high-power objective that has a short working distance and the object, even when the objectives are precisely adjusted on the objective turret so that they are "parfocal."
It can also happen that dry-type objectives having short working distances dip into immersion oil and thereby become contaminated. Moreover, in the case of known microscopes, it is necessary to lower the object stage when applying or cleaning off immersion oil and, in particular, when changing objects.
As a result, safe operation of a microscope of this type is possible only at considerably cost.